Fixing a leaky automatic transmission

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New member
Nov 5, 2023
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My Car
1973 V6 Convertible
Hi folks,

have recently gotten myself a 73 convertible with the small L6 engine and automatic transmission (believe it is the C4). Before I got the car, it hadn't been moved around much for 20 years!

I have been driving it quite a bit, putting on about 2'500 miles (or 4'000 km), and during this time had to add about 8 liters (or quarts) of automatic transmission fluid. I don't see any leaks in the garage, so work on the assumption the car loses fluid while driving.

Any recommendation how to verify and what potentially I need to change? Was thinking of replacing output shaft seal and replacing filter, though not really sure how to go about it.

Interested in your thoughts.
I agree with Bentworker. Find out where it coming from before you start throwing parts at it.

I also agree with you that the output shaft seal is a likely suspect. However, one other thing you may want to consider is the vacuum modulator, if it is bad you can be drawing transmission fluid into the intake.
If it leaked 8 liters of fluid, you would definitely see it on the underside of the car and on the garage floor.

The first thing I'd check is the vacuum line to the modulator. If it has red transmission fluid in it, then it's time for a new modulator. The diaphragm can rupture and allow the engine to draw fluid in and burn it.

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